Outcomes of Occupational Asthma and Work-Exacerbated Asthma

From 200 participants, 100 were recruited from among 102 consecutive eligible patients in the occupational lung disease clinic, and 100 others from consecutive Ontario WSIB asthma claimants. Eighty participants (40%; 60 clinic patients and 20 WSIB claimants) were classified as having sensitizer-induced OA, as follows: definite sensitizer-induced OA, 23 participants; probable sensitizer-induced OA, 26 participants; and possible sensitizer-induced OA, 31 participants, The most common agents to which sensitizer-induced OA was attributed were diisocyanates (38% of OA cases). The 87 participants (44%) in the WEA group comprised 14 clinic patients and 73 WSIB claimants. Participants with irritant-induced asthma (n = 4) and no WRA (n = 29) were excluded from the analyses. As shown in Table 1, those with OA, vs WEA, were more likely to be men (p = 0.0002) and to have a primary language other than French or English (p = 0.001). There was a greater likelihood of having never smoked in those patients with WEA. More OA patients had used Workplace Hazardous Materials Information System (WHMIS) material safety data sheets (MSDSs) and had reported a workplace screening program (31%), as expected with an occupational sensitizer, but a minority of patients had reported undergoing spirometry and responding to screening questionnaires in the workplace. Modern Inhalers are the most effective for asthma treatment.

Only 54% of WEA patients had received an assessment from a specialist (ie, pulmonary physician, allergist, or occupational medicine physician) for work-related symptoms at some time compared to all patients with OA (Table 2). The type of physician who was first consulted among 185 patients in the entire group who responded to the question on duration from symptom onset to first physician visit was a family doctor (64%), a company doctor (6%), and a physician in an emergency department or a walk-in clinic (30%).

The self-reported median time to the initial physician visit for the patients with WRA symptoms was significantly shorter in patients with WEA (< 1 month) vs those with OA (3 months; p < 0.0001). Most patients saw a doctor only when symptoms became worse or unbearable (Table 2); a minority of patients were referred by workplace screening. Only a third of patients with OA had prior knowledge of exposure to a work agent that could cause asthma, but most of these patients said it influenced their decision to see a doctor. Most patients with OA reported that coworkers had similar symptoms, and about a third of these patents were influenced by this. A similar proportion reported being influenced by a workplace health-and-safety program. More patients with WEA than with OA recognized symptoms as being work-related (p = 0.02), whereas more patients with OA than with WEA feared a diagnosis would lead to job change (p < 0.0001). More WEA patients had gone to an emergency department or a walk-in clinic initially, whereas most OA patients initially saw their family doctor. OA patients were more likely to have had an immediate referral to a specialist when WRA was suspected; almost all OA patients had seen a respiratory care physician (Table 2).

occupational asthma
The reported median time to the first suspicion of WRA by a physician was 1 year for WEA patients and 2 years for OA patients. Both groups reported income loss postdiagnosis, which was more marked among OA patients (p = 0.045). As expected, objective tests were more common in OA patients. All patients had a medical history consistent with WRA (by definition). Objective support for asthma was evident in chart review for all OA patients but only for 32% of WEA patients (p < 0.0001). Test results for the work relationship were present in most OA patients (76%) but only for 11% of WEA patients, The most common tests performed in OA patients were serial peak expiratory flow recordings at work and off work (58%), repeat methacholine challenges during work and off-work periods (49%), and skin tests using a work agent (29%). Only two patients had specific chamber challenges.

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Factors associated with a longer than median time to suspicion of WRA by the physician (as reported by the patient) for OA patients (adjusting for age and gender) [Table 4] were being the sole income earner (p = 0.05), not having knowledge of WHMIS.

MSDSs (p = 0.06), and older age (p = 0.009). For WEA patients, associated factors were as follows: physician not asking about a work association with asthma (p = 0.006); lack of knowledge of work and asthma by the worker (p = 0.007); travel distance of > 60 km to reach a specialist (p = 0.08); more dependents (p = 0.04); and longer period working (p = 0.06).

asthma

The median time to a final diagnosis of OA after the onset of work-related symptoms was 4 years (Table 5). A longer than median time to a final diagnosis was associated with age (p = 0.06). After adjusting for age and gender, a shorter than median time to diagnosis was associated with an awareness of exposure to a work agent causing asthma (p = 0.05), Surprisingly, a greater likelihood of a longer time to diagnosis was found in those patients who reported the presence of a workplace screening program (p = 0.05).

Subgroups of patients with more definite diagnoses (meeting the criteria for definite or probable OA and those with WEA who had been assessed by a specialist) showed trends similar to those of the larger groups (results not shown). Age and gender were important covariates in relationship to the time to the initial visit to a doctor. (Variables with a p value of < 0.10 in the multivariate model and potential confounders are demonstrated in the online data supplement; Table E1.) In the final model for OA, age (p = 0.04), gender (p = 0.01), and personal income (p = 0.01) remained associated with the time to the initial visit to a doctor. Years having lived in Canada was highly associated with the outcome (p < 0.01; odds ratio [OR], 1.12 [ie, the odds of having a longer time to initial visit to a doctor, greater than median of 3 months, increased approximately 12% with each additional year spent living in Canada]). A workplace screening program had borderline significance (p = 0.08). For WEA patients, gender (p = 0.04), prior knowledge of WRA (p < 0.01), and the presence of a union at the workplace (p = 0.05) were significant.

Table 1—Demographic Characteristics of Those With OA and WEA

Demographics and Other Characteristics OA Group(n = 80) WEA Group(n = 87) OR (95% CI) p Value
Clinic patient 60 (75) 14(16) 0.06 (0.03-0.14) < 0.0001
Age, yr 46.1 ± 10.5 43.7 ± 10.4 1.02 (0.99-1.05) 0.15
Male gender 47 (59) 26 (30) 0.30 (0.16-0.57) 0.0002
Unmarried 20 (25) 28 (34) 1.53 (0.77-3.02) 0.22
Income level $30,000/yrt 17 (22) 18 (21) 0.96 (0.46-2.04) 0.92
Sole source of family income 29 (36) 34 (40) 0.87 (0.46-1.63) 0.66
Primary language English or French 62 (81) 84 (97) 0.15 (0.04-0.53) 0.001
Secondary education and above 71 (90) 82 (94) 0.54 (0.17-1.73) 0.29
Smoking status Ever smoked 44 (55) 34 (39) 1.91 (1.03-3.53) 0.04
Current smoker 11 (24) 10 (29) 0.78 (0.28-2.12) 0.62
Health and safety program 69 (86) 79 (91) 0.64(0.24-1.67) 0.35
Health and safety training 48 (61) 52 (65) 0.83(0.44-1.59) 0.58
Union 46 (58) 72 (83) 0.29 (0.14-0.59) 0.0005
Know what WHMIS/MSDS are 72 (90) 78 (90) 1.04 (0.38-2.84) 0.94
WHMIS/MSDS available 60 (83) 72 (92) 0.42 (0.15-1.18) 0.09
If yes, ever used them 51 (71) 42 (54) 2.08(1.06-4.09) 0.03
Workplace screening 24 (31) 10(11) 3.42 (1.51-7.74) 0.003
Included questionnaire 15 (63) 3 (43) 2.22 (0.40-12.29) 0.41
Included PFTs 19 (79) 9 (90) 0.42 (0.04-4.16) 0.64
Diisocyanates at work 30 (38) 1(1) 0.02 (0.003-0.15) < 0.0001
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Table 2—Individual and Workplace Factors Influencing First Physician Visit and First Physician Suspicion of WRA Among OA and WEA Patients

Variables OA Group(n = 80) WEA Group(n = 87) OR (95% CI) p Value
Symptoms got worse or unbearable 74 (93) 81 (93) 0.91 (0.28-2.96) 0.88
Workplace screening program 24 (31) 10(11) 3.42 (0.16-3.27) 0.002
Referred through program 7 (29) 4 (36) 0.72 (0.51-7.64) 0.71
Aware of exposure to an agent at work 26 (33) 51 (59) 0.33 (0.18-0.62) 0.0005
Influenced by this 23 (88) 39 (75) 2.56 (0.66-9.93) 0.17
Health and safety program at work influenced visit 24 (36) 14(19) 2.49(1.16-5.36) 0.02
Coworkers with similar symptoms 58 (73) 49 (56) 2.04(1.07-3.91) 0.03
Influenced visit 20 (35) 15 (30) 1.26 (0.56-2.85) 0.58
Knowledge of OA before diagnosis 12 (15) 31 (36) 0.32 (0.15-0.69) 0.003
Influenced visit 10 (77) 27 (84) 0.62 (0.12-3.07) 0.67
Afraid of job change 64 (80) 42 (48) 4.29 (2.15-8.55) < 0.0001
Thought symptoms were work-related 52 (66) 71 (82) 0.43 (0.21-0.89) 0.02
Physician asked about work association 48 (60) 52 (62) 0.92 (0.49-1.73) 0.80
Physician first suspected work relation 47 (59) 62 (71) 0.57 (0.30-1.09) 0.09
Physician told by worker of worsening at work 71 (89) 78 (90) 0.91 (0.34-2.42) 0.85
Physician referred immediately 42 (53) 22 (26) 3.11 (1.62-6.00) 0.0006
First physician seen 0.002
Company doctor 6 (8) 1(1)
Family doctor 56 (73) 46 (56)
ED/walk-in clinic 15 (19) 35 (43)
Most specialized physician seen 0.0001
Pulmonary physician 75 (96) 35 (44)
Allergist 1(1) 5 (6)
Occupational physician 2 (3) 3 (4)
Family physician 0 (0) 29 (37)
ED physician 0 (0) 7 (9)

Table 3—Bivariate Analysis of Factors Associated With a Longer Than Median Time to First Physician Visit After Onset of Work-Related Symptoms

Variables OA Group (n = 71t) WEA Group(n = 85t)
‘ No. (%|) OR (95% CI) ‘ ‘ No. (%|) OR (95% CI)
Time to first physician visit,§ mo 8 (12.4) [3] 5.7 (21.2) [< 1]
Clinic patient 26 (48) 2.71 (0.79-9.35) 8(67) 0.25 (0.07-1.00)|
Male 25 (61) 0.40 (0.15-1.08) 13 (50) 0.35 (0.13-0.92)||
Age^ yr 46.5 (10) 1.03 (0.98-1.07) 44.6 (12) 1.01 (0.96-1.06)
Time in Canada,^ yr 43(12) 1.08 (1.03-1.14)§ 43(12.5) 0.97 (0.90-1.06)
Afraid of job loss 20 (44) 0.43 (0.15-1.23) 14 (44) 2.24 (0.85-5.94)
Afraid of job change 30 (52) 0.82 (0.23-2.96) 18 (44) 2.76(1.05-7.27)||
Afraid to lose work time 23 (43) 0.26 (0.07-0.94)|| 23 (21) 1.39 (0.38-5.06)
Took advice of a friend/family 12 (48) 0.74 (0.26-2.11) 12 (50) 2.70 (0.98-7.44)
Workplace screening program 7(41) 0.62 (0.20-1.98) 2 (20) 0.28 (0.05-1.57)
available
Aware exposed to an agent 10 (42) 0.57 (0.20-1.64) 13 (26) 0.29 (0.09-0.93)|
Presence of health and safety 28 (49) 0.88 (0.23-3.30) 20 (27) 0.02 (0.001-0.25)|
program
Prior knowledge of OA 3(27) 0.25 (0.05-1.20) 3 (10) 0.12 (0.03-0.45)|
Symptoms thought work-related 19 (42) 0.27 (0.09-0.86)|| 21 (30) 0.43 (0.13-1.42)
Highest education greater than 31 (50) 0.45 (0.08-2.64) 3(60) 0.51 (0.07-3.63)
primary
Personal income > $30,000/yr# 26 (48) 0.39 (0.09-1.62) 19 (29) 0.31 (0.10-0.99)|
Sole income earner 13 (59) 1.54 (0.54-4.41) 8(24) 0.46 (0.17-1.29)
First language English or French 34 (60) 26.97 (3.57-203.87)|| 27 (33) 0.35 (0.02-6.59)
Unmarried 12 (71) 0.28 (0.08-0.96)|| 7 (26) 1.50 (0.53-4.25)
Presence of health and safety 30 (50) 0.90 (0.22-3.79) 25 (33) 0.68 (0.14-3.32)
committee
Health and safety training 21 (48) 0.69 (0.25-1.92) 11 (22) 0.23 (0.08-0.69)|
Presence of a union 18 (47) 0.77 (0.29-2.05) 19 (27) 0.23 (0.07-0.77)||
Know what WHMIS/MSDS are 35 (55) 5.92 (0.87-40.09) 25 (33) 0.65 (0.13-3.25)
Distance from specialist > 60 km 10 (59) 1.47 (0.47-4.66) 8(62) 3.85 (0.99-14.95)
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Table 4—Bivariate Analysis of Factors Associated With a Longer Than Median Time to First Physician Suspicion of WRA

Variables OA Group (n = 79f) WEA Group (n = 35f)
No. (%{) OR (95% CI) No. (%{) OR (95% CI)
Time to first physician suspicion,§ yr 3.8 (4.3) [2] 3.7 (7.3) [1]
Clinic patient 33 (56) 0.37 (0.12-1.16) 10 (77) 0.02 (0.001-0.28)|
Age,! yr 49.5 (8.7) 1.07 (1.02-1.12)| 48.7 (7.5) 1.08 (0.99-1.17)
MD asked about work association 27 (56) 2.33 (0.86-6.31) 3(14) 0.06 (0.01-0.45)|
Prior knowledge of OA 3(25) 0.46 (0.11-2.02) 1(11) 0.02 (0.001-0.34)||
Highest education greater than 32 (46) 0.64 (0.10-4.00) 11 (33) 0.28 (0.01-13.44)
primary
Sole income earner 19 (66) 2.69 (0.99-7.31) 3 (20) 0.09 (0.01-0.70)|
Unmarried 11 (55) 0.72 (0.24-2.15) 2 (20) 5.23 (0.74-36.72)
Know what WHMIS/MSDS are 32 (45) 0.12 (0.01-1.13) 11(35) 0.34 (0.02-7.43)
Distance from specialist > 60 km 10 (56) 1.96 (0.63-6.04) 5 (63) 8.58 (0.78-94.91)
Dependents at symptom onset,! No. 1.1 (1.2) 0.84 (0.58-1.24) 1.6 (1.2) 2.84(1.05-7.65)||
Work-yr! 17.2 (9.2) 1.03 (0.98-1.08) 18.3 (10.6) 1.09(1.00-1.19)

Table 5—Bivariate Analysis of Factors Associated With a Longer Than Median Time to Final Diagnosis of OA From Onset of WRA Symptoms

Variables OA Group (n = 77f)
No. (%|) OR (95% CI)
Time to final diagnosis,§ yr 5.0 (4.9) [4]
Clinic patient 33 (58) 0.33(0.11-1.02)
Age, || yr 48.3 (9.4) 1.04(1.00-1.09)
Took advice of friend/family 10 (34) 0.41 (0.15-1.11)
Workplace screening program 16 (67) 2.88(1.00-8.27)!
Aware exposed to an agent 8(31) 0.35 (0.12-0.99)!
Physician visits before suspecting OA,|| No. 4.6 (8.6) 1.25 (1.02-1.54)!